Lockdown system for use in a wellhead assembly

ABSTRACT

A wellhead assembly having an outer tubular, an inner tubular inserted into the outer tubular, an annular space between the inner and outer tubulars, a lock ring in the annular space, and an activation ring that axially strokes between the lock ring and one of the tubulars. The lock ring selectively locks together the inner and outer tubulars when the activation ring slides between the lock ring and the one of the tubulars. The surface of the activation ring that contacts lock ring is contoured so that an interface surface between the activation ring and lock ring when the lock ring is in its locked position, is offset an angle from an axis of the wellhead that is less than an offset between the axis of the wellhead and an interface surface between the activation ring and lock ring when the activation ring is stroking downward.

BACKGROUND

1. Field of Invention

The invention relates generally to a system and method for lockingtogether tubulars in a wellhead assembly.

2. Description of Prior Art

Wellheads used in the production of hydrocarbons extracted fromsubterranean formations typically comprise a wellhead assembly attachedat the upper end of a wellbore formed into a hydrocarbon producingformation. Wellhead assemblies usually provide support hangers forsuspending production tubing and casing into the wellbore. The casinglines the wellbore, thereby isolating the wellbore from the surroundingformation. The tubing typically lies concentric within the casing andprovides a conduit therein for producing the hydrocarbons entrainedwithin the formation.

Wellhead assemblies also typically include a wellhead housing adjacentwhere the casing and tubing enter the wellbore, and a production treeatop the wellhead housing. The production tree is commonly used tocontrol and distribute the fluids produced from the wellbore andselectively provide fluid communication or access to the tubing, casing,and/or annuluses between the tubing and casing. Valves assemblies aretypically provided within wellhead production trees for controllingfluid flow across a wellhead, such as production flow from the boreholeor circulating fluid flow in and out of a wellhead.

Seals are used between inner and outer wellhead tubular members tocontain internal well pressure. The inner wellhead member may be atubing hanger that supports a string of tubing extending into the wellfor the flow of production fluid. The tubing hanger lands in an outerwellhead member, which may be a wellhead housing, a production tree, ora tubing head. A packoff or seal seals between the tubing hanger and theouter wellhead member. Alternately, the inner wellhead member might bean isolation sleeve secured to a production tree. A seal or packoffseals between the isolation sleeve and a casing hanger located withinthe wellhead housing.

A variety of seals of this nature have been employed in the prior art.Prior art seals include elastomeric and partially metal and elastomericrings. Prior art seal rings made entirely of metal for formingmetal-to-metal seals are also employed. The seals may be set by arunning tool, or they may be set in response to the weight of the stringof casing or tubing. One type of prior art metal-to-metal seal has innerand outer walls separated by a conical slot. An energizing ring ispushed into the slot to deform the inner and outer walls apart intosealing engagement with the inner and outer wellhead members. Thedeformation of the inner and outer walls exceeds the yield strength ofthe material of the seal ring, making the deformation permanent.Sometimes a lockdown ring is provided in the annular space between thetubulars, which is put into a position that locks the tubulars to oneanother when the seal is set.

SUMMARY OF THE INVENTION

Provided herein is an example of a wellhead assembly. In one example, awellhead assembly includes an axis, an outer tubular, an inner tubularinserted into the outer tubular and defining an annular space betweenthe inner tubular and outer tubular, and a lock ring in the annularspace that is moveable from an unlocked position into a locked position.The wellhead assembly of this embodiment also includes an activationring having a profiled surface that is axially slidable against and incontact with the lock ring to define a contact interface that is offsetan angle from the axis when the lock ring is in the locked position, andto define a contact interface that is offset an angle from the axis whenthe lock ring is in the unlocked position, so that the angle when thelock ring is in the locked position is less than the angle when the lockring is in the unlocked position. Optionally, a portion of the profiledsurface is curved that is in contact with the lock ring when the lockring is in the unlocked position, and a portion of the profiled surfacethat is in contact with the lock ring when the lock ring is in thelocked position is substantially linear. In one example embodiment, thelock ring is set radially inward from the outer tubular when in theunlocked position, and the lock ring comprises a protrusion that engagesa depression formed in an inner radial surface of the outer tubular.Alternatively, the lock ring is set radially outward from the innertubular when in the unlocked position, and the lock ring has aprotrusion that engages a depression formed in an outer radial surfaceof the inner tubular. In an alternate embodiment, the wellhead furtherincludes a seal assembly that transfers a downward axial force to anupper end of the activation ring and that is energized by an energizingforce. The force applied to the activation ring that slides theactivation ring along the lock ring may urge the lock ring from theunlocked position to the locked position, and the energizing force canbe greater than the force applied to the activation ring. In oneexample, the outer tubular is a wellhead housing and the inner tubularis a tubing hanger.

Also provided herein is a system for locking together tubulars that aredisposed in a wellhead assembly. In this example the system includes alock ring that axially rests on one of the tubulars and selectivelyengages an adjacent tubular thereby axially locking together the one ofthe tubulars and the adjacent tubular. Also included is an activationring axially moveable to between the lock ring and the one of thetubulars and having a surface in sliding contact with the lock ring thattransitions from a curved profile to a linear profile as the activationring moves to between the lock ring and the one of the tubulars. In anexample embodiment of the system, the activation ring contacts the lockring along an interface that is offset from an axis of the wellheadassembly by an angle up to about 5 degrees when the lock ring isengagement with the adjacent tubular. Optionally, the activation ringcontacts the lock ring along an interface that is offset from an axis ofthe wellhead assembly by an angle that ranges from at least about 5degrees to about 30 degrees when the curved profile is in contact withthe lock ring. The one of the tubulars can be a tubing hanger and theadjacent tubular can be a wellhead housing. In an alternate example, theone of the tubulars can be a wellhead housing and the adjacent tubularcan be a tubing hanger. Optionally, an upper end of the activation ringis in axial contact with a seal assembly, where the seal assembly isenergized with an axial force that exceeds a force applied to slide theactivation ring from a position above the lock ring to a positionadjacent the lock ring.

Yet further provided herein is a method of locking together tubulars ina wellhead assembly. One example embodiment of the method includesproviding a lock ring on a lateral surface of one of the tubulars,applying a force onto the lock ring in a direction oblique with an axisof the wellhead assembly to radially urge the lock ring towards anadjacent tubular, changing the direction of the force to besubstantially perpendicular to the axis and engaging the lock ring withthe adjacent tubular, and retaining the lock ring in engagement with theadjacent tubular by continuing to apply the force in a directionsubstantially perpendicular to the axis. The method may further includeproviding an activation ring having a contact surface that transitionsfrom a curved portion to a linear portion. In one example, the step ofapplying a force onto the lock ring in a direction oblique with an axisof the wellhead assembly involves axially urging the activation ring sothe curved portion slides against a side of the lock ring. In anoptional embodiment, the step of applying a force onto the lock ring ina direction perpendicular to an axis of the wellhead assembly includesaxially urging the activation ring so the linear portion slides againsta side of the lock ring. In an example, the step of continuing to applythe force in a direction substantially perpendicular to the axisincludes retaining the activation ring adjacent the lock ring so thelinear portion is in contact with a side of the lock ring.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are side sectional views of an example of couplingtogether tubulars in a wellhead assembly in accordance with the presentinvention.

FIGS. 2A-2C are side sectional detailed views of operation of a lockingmechanism of FIGS. 1A and 1B in accordance with the present invention.

FIG. 3 is a side partial sectional view of an example embodiment of thewellhead assembly of FIGS. 1A and 1B set over a wellbore in accordancewith the present invention.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying drawings inwhich embodiments are shown. The method and system of the presentdisclosure may be in many different forms and should not be construed aslimited to the illustrated embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey its scope to those skilled in the art.Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosureis not limited to the exact details of construction, operation, exactmaterials, or embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. In the drawingsand specification, there have been disclosed illustrative embodimentsand, although specific terms are employed, they are used in a genericand descriptive sense only and not for the purpose of limitation.Accordingly, the improvements herein described are therefore to belimited only by the scope of the appended claims.

FIG. 1A is a side sectional view of one example embodiment of a wellheadassembly 10 that includes a portion of a wellhead housing 12 adjacent atubing hanger 14. The wellhead housing 12 and tubing hanger 14 aregenerally tubular members that are spaced apart. An example of a sealassembly 16 is illustrated set within an annulus 18 that is between thetubing hanger 14 and wellhead housing 12. The embodiment of the sealassembly 16 includes an annular seal ring 20 insertable into the annulus18. The seal ring 20 of FIG. 1A has an inner leg 22, which as providedin the sectional view is an elongate member that extends generallyparallel with an axis A_(X) of the wellhead assembly 10. The example ofthe seal ring 20 also includes an outer leg 24; which also extendssubstantially parallel with the axis A_(X) and is longer than the innerleg 22. The outer leg 24 is set radially outward from the inner leg 22to define an annular space 26 set between the inner and outer legs 22,24. The inner and outer legs 22, 24 are connected to one another ontheir respective lower ends by a cross piece that also defines a lowersurface of the space 26. An energizing ring 28 is shown having a lowerend inserted into an upper end of the space 26. In an example, axiallyurging the seal assembly 20 into annulus 18 then inserting energizingring 28 into space 26 urges legs 22, 24 radially outward from oneanother thereby creating a pressure barrier in the annulus 18. Aring-like collar 30 is shown circumscribing a portion of the energizingring 28 and threadingly engaged with an upper end of the outer leg 24.

Further illustrated in the example of the wellhead assembly 10 of FIG.1A is an annular activation ring 32, which is set in the annulus 18below the seal assembly 20. In the example of FIG. 1A, the lower end ofthe seal assembly 20 rests on an upper end of the activation ring 32.Below the activation ring 32 is a lock ring 34 for axially lockingtogether the wellhead housing 12 and tubing hanger 14. Referring now toFIG. 2A, illustrated in detailed sectional view is an example of theactivation ring 32 and lock ring 34. In the example of FIGS. 1A and 2A,the lock ring 34 is in an unlocked configuration, thus the wellheadhousing 12 and tubing hanger 14 may move axially with respect to oneanother. As shown in FIG. 2A, a surface of the activation ring 32 facingaxis A_(X) defines an inner surface 36 that is shown having a transition38 where a radius of the surface 36 changes. Opposite the inner surface36 is an outer surface 40 shown having a lower portion 42 thattransitions into an upper portion 44. The transition 46 at the upper endof upper portion 44 defines where a change in length of radius of theouter surface 40 takes place.

Profiles 48 are shown formed on the outer surface 40 and abovetransition 46 to define a handle 50 for raising and lowering theactivation ring 32 within the annulus 18 (FIG. 1A). In the example ofFIG. 2A, a line L₁ is shown extending tangentially across upper portion44 illustrating in the example of FIG. 2A that the outer surface 40 isgenerally linear along upper portion in the axial direction. Incontrast, outer surface 40 along lower portion 42 is curved and in someportions thereof maintains a consistent radius. A line L₂ is showntangentially across a portion of an inner surface of the lock ring 34.In one example embodiment, the line L₂ is at about 20 degrees to about35 degrees offset from axis A_(X).

Still referring to FIG. 2A, an outer surface 54 of the lock ring 34 isshown having protrusions 56 that extend radially outward and away frominner surface 52. Referring back to FIG. 1A, the protrusions 56 areprofiled to correspond to depressions 58 shown formed along an innersurface 60 of the wellhead housing 12 and adjacent lock ring 34. Furtherillustrated in FIG. 1A are wickers 62, 64 shown respectively formed onthe inner surface 60 of the wellhead housing 12 and an outer surface 66of the tubing hanger 14. In an embodiment, the wickers 62, 64 areridge-like members formed in the surfaces 60, 66, so that when the seal20 is set in the annulus 18, the wickers 62, 64 deform respective outersurfaces of the inner leg 22 and outer leg for enhancing the sealingfunction of the seal assembly 20.

FIG. 1B illustrates in side sectional view an example of the lock ring34 set in a locked position and in engagement with the depressions 58 onthe wellhead housing 12. Further illustrated in FIG. 1B is that a lowerend of the lock ring 34 rests on a shoulder 67 defined where the outersurface 66 of the tubing hanger 14 juts radially outward and away fromaxis A_(X). Engaging the protrusions 56 with the depressions 58 axiallyretains the lock ring 34 in place. Also, by contacting the shoulder 67with lower end of the block ring 34, the tubing hanger 14 is preventedfrom moving axially upward with respect to the wellhead housing 12 bythe axially static lock ring 34. Further in the example of FIG. 1B, thelock ring 34 engages the profiles 58 by being moved radially outwardfrom axis A_(X) by downward axial movement of the activation ring 32.Thus, retaining the activation ring 32 in the position of FIG. 1B, thetubing hanger 14 is axially constrained to the wellhead housing 12.

A detailed example of interaction between the activation ring 32 andlock ring 34 in the locked position is illustrated in side sectionalview in FIGS. 2B and 2C. In FIG. 2B, shown is an example of theactivation ring 32 having a force F applied to its upper end therebyslidingly urging the activation ring 32 to a position adjacent the lockring 34 (FIG. 2C). In one example, the activation ring 32 and lock ring34 are substantially coaxial when the lock ring 34 is in the lockedposition. In the example of FIG. 2B, the lower curved portion 42 of theactivation ring 32 is in contact with the inner surface 52 of the lockring 34. As such, a resultant force F_(R) is exerted against the lockring 34 and shown being in a direction generally oblique to the axisA_(X). With further downward movement of the activation ring 32, thedirection of resultant force F_(R) rotates from its oblique orientationand to one that is close to being substantially perpendicular to axisA_(X) (FIG. 2). In the example of FIG. 2B, a portion of line L₃ extendsalong a contact interface between the activation ring 32 and lock ring34. Similarly, line L₄ in FIG. 2C is drawn along a contact interfacebetween the activation ring 32 and lock ring 34 when the activation ring32 is substantially adjacent lock ring 34. As shown, line L₄ is at anoffset angle from axis A_(X) that is less than an offset angle betweenL₃ and axis A_(X) (FIG. 2B).

An advantage of the curved lower surface 42 is that the lock ring 34 maybe urged radially outward into its locked configuration with thewellhead housing 12 by a stroke distance of the activation ring 32 thatis shorter than a corresponding stroke distance in instances where thelower portion 42 is linear. Moreover, by transitioning the outer surface40 of the activation ring 32 from a curved lower portion 44 to a linearupper portion 44, the resultant force F_(R) has a reduced axialcomponent exerted from the lock ring 34 onto the activation ring 32. Assuch, more force from the lockdown system may be distributed towardsretaining the tubing hanger 14 rather than maintaining the lock ring 34in its locked position.

FIG. 3 is a side partial sectional view of one example of the wellheadassembly 10 shown set over a wellbore 68, where the wellbore 68 extendsthrough a formation 70. In the example of FIG. 3, an example of alockdown assembly 71 is schematically illustrated for locking the tubinghanger 14 to the wellhead housing 12. In the example of FIG. 3, thelockdown assembly 71 includes examples of the activation ring andlockdown ring as described above. Further illustrated in FIG. 3 is astring of tubing 72 that depends downward into the bore hole 68 from thetubing hanger 14.

An additional advantage of the lockdown assembly illustrated herein isthat by transitioning the outer surface of the retaining ring 32, axialforces required for retaining the lockdown ring 34 in its lockedposition are reduced that in turn allows for higher preloads on a sealassembly 20 (FIG. 1A). Thus, the lock ring 34 can be set at an axialforce below that which may initiate energizing of a seal set in theannulus 18.

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the spirit of the present invention disclosed hereinand the scope of the appended claims.

What is claimed is:
 1. A wellhead assembly comprising: an axis; an outertubular; an inner tubular inserted into the outer tubular and definingan annular space between the inner tubular and outer tubular; a lockring in the annular space that is moveable from an unlocked positioninto a locked position; an activation ring having a profiled surfacethat is axially slidable against and in contact with the lock ring todefine a contact interface that is offset an angle from the axis whenthe lock ring is in the locked position, and to define a contactinterface that is offset an angle from the axis when the lock ring is inthe unlocked position, so that the angle when the lock ring is in thelocked position is less than the angle when the lock ring is in theunlocked position.
 2. The wellhead assembly of claim 1, wherein aportion of the profiled surface is curved that is in contact with thelock ring when the lock ring is in the unlocked position, and wherein aportion of the profiled surface that is in contact with the lock ringwhen the lock ring is in the locked position is substantially linear. 3.The wellhead assembly of claim 1, wherein the lock ring is set radiallyinward from the outer tubular when in the unlocked position, and whereinthe lock ring comprises a protrusion that engages a depression formed inan inner radial surface of the outer tubular.
 4. The wellhead assemblyof claim 1, wherein the lock ring is set radially outward from the innertubular when in the unlocked position, and wherein the lock ringcomprises a protrusion that engages a depression formed in an outerradial surface of the inner tubular.
 5. The wellhead assembly of claim1, further comprising a seal assembly that transfers a downward axialforce to an upper end of the activation ring and that is energized by anenergizing force.
 6. The wellhead assembly of claim 5, wherein a forceapplied to the activation ring that slides the activation ring along thelock ring and urges the lock ring from the unlocked position to thelocked position, and wherein the energizing force is greater than theforce applied to the activation ring.
 7. The wellhead assembly of claim1, wherein the outer tubular comprises a wellhead housing and the innertubular comprises a tubing hanger.
 8. A system for locking togethertubulars that are disposed in a wellhead assembly comprising: a lockring that axially rests on one of the tubulars and selectively engagesan adjacent tubular thereby axially locking together the one of thetubulars and the adjacent tubular; an activation ring axially moveableto between the lock ring and the one of the tubulars and having asurface in sliding contact with the lock ring that transitions from acurved profile to a linear profile as the activation ring moves tobetween the lock ring and the one of the tubulars.
 9. The system ofclaim 8, wherein the activation ring contacts the lock ring along aninterface that is offset from an axis of the wellhead assembly by anangle up to about 5 degrees when the lock ring is engagement with theadjacent tubular.
 10. The system of claim 8, wherein the activation ringcontacts the lock ring along an interface that is offset from an axis ofthe wellhead assembly by an angle that ranges from at least about 5degrees to about 30 degrees when the curved profile is in contact withthe lock ring.
 11. The system of claim 8, wherein the one of thetubulars is a tubing hanger and the adjacent tubular is a wellheadhousing.
 12. The system of claim 8, wherein the one of the tubulars iswellhead housing and the adjacent tubular is a tubing hanger.
 13. Thesystem of claim 8, wherein an upper end of the activation ring is inaxial contact with a seal assembly, where the seal assembly is energizedwith an axial force that exceeds a force applied to slide the activationring from a position above the lock ring to a position adjacent the lockring.
 14. A method of locking together tubulars in a wellhead assemblycomprising: providing a lock ring on a lateral surface of one of thetubulars; applying a force onto the lock ring in a direction obliquewith an axis of the wellhead assembly to radially urge the lock ringtowards an adjacent tubular; changing the direction of the force to besubstantially perpendicular to the axis and engaging the lock ring withthe adjacent tubular; and retaining the lock ring in engagement with theadjacent tubular by continuing to apply the force in a directionsubstantially perpendicular to the axis.
 15. The method of claim 14,further comprising providing an activation ring having a contact surfacethat transitions from a curved portion to a linear portion.
 16. Themethod of claim 15, wherein the step of applying a force onto the lockring in a direction oblique with an axis of the wellhead assemblycomprises axially urging the activation ring so the curved portionslides against a side of the lock ring.
 17. The method of claim 15,wherein the step of applying a force onto the lock ring in a directionperpendicular to an axis of the wellhead assembly comprises axiallyurging the activation ring so the linear portion slides against a sideof the lock ring.
 18. The method of claim 15, wherein the step ofcontinuing to apply the force in a direction substantially perpendicularto the axis comprises retaining the activation ring adjacent the lockring so the linear portion is in contact with a side of the lock ring.